Many communications systems of today operate over a very broad spectrum of frequencies. Such systems are commonly referred to as “broadband systems”. FIG. 1 is an illustration of a transceiver 100 used in one such broadband system. The transceiver 100 of FIG. 1 includes a transmit section 102 and a receive section 104. The transmit section 102 includes a transmit processor 106, digital to analog converter (DAC) 108, set of analog filters 110 and a power amplifier 112. The receive section 104 includes a low noise amplifier (LNA) 114, analog filters 116, analog to digital converter (ADC) 118, and a receive processor 120. Broadband systems are more common today than they were in the past because of the increase in the need to communicate large amounts of data. The continuing growth of the internet and use of multimedia technologies have contributed to the growth in the amount of data that needs to be communicated.
One particular industry in which there is a need to communicate large amounts of data is the entertainment industry. The development and evolution of home entertainment networks allows entertainment content to be delivered to a home from a content provider. Such content can then be distributed throughout a home or multi-dwelling unit (MDU) over a home entertainment network.
Communication of entertainment content, such as high definition video streams, requires networks that have very large capacity. To achieve the necessary capacity, many modern communications and content distribution networks rely upon broadband systems, such as satellite television networks and networks that operate in accordance with the well-known Multimedia over Coax Alliance (MoCA) standard or the well-known Data Over Cable Service Interface Specification (DOCSIS) standard.
The advantage of broadband systems is that they allow content to be spread over the large expanse of frequencies that are available. The disadvantage of broadband systems is that there is a greater chance that interference might be present in the frequencies used to communicate data over the system. That is, there is a limited range of frequencies that are practical for use in communicating information, whether that information is being communicated wirelessly, such as is the case in satellite transmission systems, or over wires, such as is the case with cable television (CATV) networks and fiber optic networks. In some cases, it is desirable to receive content over both a CATV network and a satellite network. In other cases, a MoCA network is used to distribute content that is received by a satellite receiver. In other cases, the well-known DOCSIS protocol is used together with MoCA to distribute information and content throughout a home or group of apartments within an MDU. Because these systems operate over very broad range of frequencies, it is difficult to allocate unique frequencies to each.
Because more than one broadband system might be in use, transmissions from one system may interfere with the reception of transmission from another broadband system. Furthermore, harmonics created by one broadband system might be occur in the frequencies used by another broadband system. In the past, when communicating over relatively narrow band communication systems, it was less likely that one system would create interference for other systems. Frequencies have traditionally been allocated for narrowband systems to minimize the risk of interference. However, in broadband systems, there is a greater chance that the frequencies used by one broadband system will interfere with the reception of signals of other broadband systems. This problem is further exacerbated by a increased likelihood that transmitters and receivers from different broadband systems might be integrated together into a relatively small package. In many cases today, the transmitter of one broadband system shares a substrate (silicon or printed circuit board) with the receiver from another broadband system.
In one case in particular, MoCA has an operating range of 1.5 GHz. DOCSIS 3.1 has an operating frequency range of close to 2 GHz. In allocating this frequency band, it was hard to find discrete bands in which each can operate without interference. In the case of MoCA and satellite reception, satellite transmission systems that communicate television content to homes operate at frequencies that are within the range of harmonics of the signals used to communicate over MoCA.
This problem is particularly acute when the transmitter of one broadband system is co-located with, or located in close proximity to, the receiver of another broadband system. In such cases, it can be very difficult to prevent the high power transmissions generated by the transmitter of one system (and/or harmonics generated by one system) from interfering with the reception of signals to be received by the other system.
There are essentially two ways in which to prevent interference. The first way is to provide discrete times at which each system transmits and receives. This is commonly referred to as “time diversity”. The second way is to provide discrete frequencies over which the systems transmit and receive such that the two systems do not transmit on the same frequency. This is commonly referred to as “frequency diversity”. For example, one way in which these problems are solved is to try to coordinate the transmission and reception of signals by the different broadband systems. In some cases, transmissions by a first broadband system are “blanked” during times when a second broadband system is attempting to receive signals.
In other systems, the particular range of frequencies is limited to less than the full spectrum that would otherwise be available to each broadband system. It should be noted that in addition to the fundamental frequencies, harmonics of those frequencies used for transmission can be sufficiently powerful that they interfere with attempts by other systems to transmit at those harmonic frequencies.
A third way to address the problem of transmission signals generated by a first broadband system impinging upon the reception of signals transmitted by another broadband system is to use a different medium for the transmission of signals by each broadband system. The definition of “different medium” can include two coaxial cables that are not coupled to one another. However, the definition may also include the case in which a filter or diplexer is used to block signals from one medium from coupling to the other medium. In this case, the medium used by one broadband system must be sufficiently isolated from the medium used by another system so that no interference is generated between the two broadband systems. Because the receivers of such broadband systems tend to be relatively sensitive, the isolation between the mediums must be very high. This can be difficult to achieve due to leakage and cross-talk between the broadband systems. That is, diplexers and physical distance between components of the two broadband systems are typically used to isolate one broadband system from another. However, there remain challenges to achieving the required isolation in systems in which the transmitter of one broadband system is in close proximity to the receiver of another broadband system.
The first two of these techniques (i.e., using time or frequency diversity) for dealing with interference between broadband systems result in a reduction in the available resources (i.e., reduced bandwidth) that can be used to communicate information. The third technique (independent medium) presents challenges to achieving the required isolation.
Therefore, there is a need for a technique that allows a first broadband system to transmit in close proximity to the receiver of a second broadband system on overlapping frequencies without the transmissions of the first broadband system interfering with reception by the second broadband system.